As a result of the cessation of the use of asbestos in automotive disc brake pads there has been a significant change in the pattern of wear in disc brakes. The use of new non-asbestos materials has required a change in the hardness of the steel used on the disc rotor and this has resulted in increased wear of the disc rotor (“disc”) itself. The need to replace disc brakes and the frequency of replacement has become a more common element of vehicle maintenance and a significant cost centre. The practice of machining discs has become uncommon as the discs tend to wear quickly to a thickness outside of the manufacturers specification hence replacement is required. The vast majority of brakes are steel, although there are a small number of ceramic or carbon fibre discs these tend to be for racing or belong to exotic marques.
Most cars have some form of sensing that indicates wear in the disc pad, usually in the form of a sensor that is attached to the pad and become exposed when the friction material is worn past a certain point. In contrast currently there is no simple means of measuring the thickness of the disc without the removal of the wheel in order to access the disc.
The object of the present invention is to provide a device and method which can be used to conveniently measure the thickness of a disc brake rotor insitu on a stationary vehicle. As will be described in more detail below, the most convenient implementation of the invention can be carried out by modifying known forms of digital vernier devices. Digital vernier devices are readily available and these devices typically have a pair of jaws at one end referred to for convenience as the proximal end and a slider body located adjacent to the jaws. Sometimes a probe is located at the distal end for measurement of the depth of a bore.
A device of conventional construction cannot conveniently be used to measure the thickness of a disc brake rotor without first removing the road wheel of the vehicle because it would be difficult to position the jaws so that they could engage opposite sides of the disc brake. Also, many vehicles have a dust cover inwardly adjacent to the rotor which could also interfere with positioning of jaws of a known form of calliper. Further, when disc brakes wear, they tend to form a lip at the outer periphery of the rotor which is not engaged by the disc brake pad and therefore does not wear. In a normal vernier calliper, the jaws are straight and the jaws would tend to engage the lip rather than the operating surfaces of the disc rotor so that an accurate reading of the wear on the disc brake could not be obtained.